While the density meter to be disclosed herein is capable of determining the density of any test fluid, the particular embodiment to be described has been developed for the purpose of determining accurately the density of a drilling fluid utilized in well-drilling operations. This drilling fluid, sometimes called "drilling mud", has a number of basic purposes in the drilling of a well. One purpose is to cool and lubricate the bit and the string. Another is to carry up to the surface the bore-hole material which is produced as a result of the drilling operation. A third purpose is to deposit a tough and low-permeability filter cake against the sides of the bore-hole and thus reduce the invasion of the fluid phase into the formation and control the loss of the fluid phase down hole. A fourth is to overbalance formation pore-pressures with sufficient hydrostatic head in order to control well flowing. A fifth is for control of corrosion of the drill string and bit, and a sixth is to buoyantly support the drill string.
Due to geothermal heat in the surrounding formations, the temperature of the drilling fluid can rise as high as 600.degree. F. or more. The pressure of the drilling fluid is a function of depth and density, and for very deep wells, the pressure placed upon the drilling fluid at the bottom of the fluid can be as high as 20,000 psi or more.
At least some of the performance characteristics of a given drilling fluid are influenced by or depend upon the density of the fluid. An example is the purpose of buoyantly supporting the drill string. Also, the total pressure developed in the fluid, which is a factor in over balancing formation pore pressures, is obviously dependent upon the density.
It is therefore of considerable benefit to know accurately the density of a given drilling fluid, preferably at elevated temperatures and pressures.
The prior art contains the following patents of interest:
U.S. Pat. No. 4,117,716, issued Oct. 3, 1978 to Simon PA1 U.S. Pat. No. 3,553,636, issued Jan. 5, 1971 to Baird PA1 U.S. Pat. No. 3,690,184, issued Sept. 12, 1972 to Chadenson PA1 U.S. Pat. No. 3,368,393, issued Feb. 13, 1968 to Wilson et al PA1 U.S. Pat. No. 2,279,254, issued Apr. 7, 1942 to Irwin PA1 U.S. Pat. No. 3,782,199, issued Jan. 1, 1974 to Bell PA1 U.S. Pat. No. 3,008,332, issued Nov. 14, 1961 to Charbonnier et al. PA1 a main body, PA1 a vertically elongated chamber in said main body adapted to contain a test fluid, the chamber having a bottom end and a top end, PA1 a passageway in said main body connecting to the chamber adjacent the bottom end of the chamber, the passageway vertically spanning at least a bottom portion of the chamber and leading to the exterior of said main body, PA1 the chamber containing in its lower end a liquid which is immiscible with and denser than said test fluid, the liquid also occupying at least part of said passageway, PA1 access means communicating with the chamber at two longitudinally spaced apart locations therealong, whereby test fluid may be admitted to and evacuated from the chamber, PA1 and measuring means for determining the location of the top surface of the liquid in the chamber, said measuring means including an ultrasonic device at the bottom of the chamber adapted to generate an ultrasound signal in the said liquid and to detect the return of the echo of said signal from the said top surface of the liquid in the chamber, the access means including an entry near the top of the chamber and an exit near the bottom of the chamber. PA1 providing a main body having a vertically elongated chamber adapted to contain the test fluid, the chamber having a bottom end and a top end, a passageway in said main body connecting to the chamber adjacent the bottom end of the chamber, the passageway vertically spanning at least a bottom portion of the chamber and leading to the exterior of said main body, PA1 placing in the lower end of the chamber and in at least part of the passageway a liquid which is immiscible with and denser than said test fluid, PA1 measuring the vertical position of the top surface of the liquid by generating an ultrasound signal in the liquid at the bottom of the chamber and detecting the return of the echo of said signal from the top surface of the liquid in the chamber, PA1 admitting the test fluid to the chamber through an access port near the top end thereof until it fills the chamber above the liquid to the level of the access port, thereby expelling some of the liquid into said passageway and lowering the top surface of the liquid in the chamber, PA1 measuring the new vertical position of the top surface of the liquid by again generating an ultrasound signal in the liquid at the bottom of the chamber and detecting the return of the echo of said signal from the top surface of the liquid in the chamber, PA1 and calculating the density of the test fluid on the basis of the depression of the top surface of the liquid by the weight of the test fluid, the height of the test fluid above the liquid, and the geometry of the passageway. PA1 providing a main body having a vertically elongated chamber adapted to contain the test fluid, the chamber having a bottom end and a top end, a passageway in said main body connecting to the chamber adjacent the bottom end of the chamber, the passageway vertically spanning at least a bottom portion of the chamber and leading to the exterior of said main body, PA1 placing in the lower end of the chamber and in at least part of the passageway a liquid which is immiscible with and denser than said test fluid, PA1 measuring the vertical position of the top surface of the liquid by generating an ultrasound signal in the liquid at the bottom of the chamber and detecting the return of the echo of said signal from the top surface of the liquid in the chamber, PA1 continuously circulating the test fluid through the chamber between an inlet and an outlet which are spaced apart longitudinally, the uppermost of the inlet and outlet establishing the top of the column of test fluid, PA1 continuously measuring the vertical position of the top surface of the liquid by again generating an ultrasound signal in the liquid at the bottom of the chamber and detecting the return of the echo of said signal from the top surface of the liquid in the chamber, PA1 and calculating from time to time the density of the test fluid on the basis of the depression of the top surface of the liquid by the weight of the test fluid, the height of the test fluid above the liquid, and the geometry of the passageway.
Because none of the prior art patents listed above proposes to measure the density of a test fluid under conditions of elevated temperature and pressure, they do not encounter and do not have to solve the problems associated with that determination. These problems will be more clearly apparent during the subsequent detailed description of the present invention.